This Phase 3, open label safety and efficacy study will be performed at participating sites worldwide. The study will enroll ~ 220 boys with nonsense mutation dystrophinopathy who participated in a previous Phase 3 study of ataluren (Protocol # PTC124-GD-020-DMD). Patients will receive 10, 10, 20 mg/kg of ataluren TID at morning, midday, and evening for approximately 96 weeks. Study assessments will be performed at clinic visits every 12 weeks.